Seems poor headline writing. The fact that it was on his testicles is hardly the relevant fact, though certainly an interesting detail.
His willingness to show off his testicles doesn’t seem too strange, northern Europeans have much fewer hangups about nudity than Americans. His willingness to show off a swastika tattoo is deeply shocking.
Short-arm inspection, and the reverse “Ben Dover and Spread 'Em” looky-loos are fairly typical with army types. Especially infantry, with all that potential for rashes.
Austria is not in Northern Europe, but the rest of what you said applies to some level. That said, people are not in the habit of randomly showing off their private parts to their friends.
Anyway, even in areas where nudity isn’t a shocker, completely nude people are not commonplace, and showing off male genitalia is rare. Even at a FKK beach, you would not show off you scrotum. People would perhaps register if you have tattooed balls, but in my opinion, it would have been really unusual for most people to inspect even if they thought it would be a swastika.
You have to be extremely stupid to get that level of attention.